The present invention relates to a safety device for a syringe which has a syringe body, a plunger assembly and a needle, where the device includes a support sleeve suitable for retaining the body of the syringe relative thereto, a protection sleeve and at least one retaining tab rigidly connected to the protection sleeve and suitable for occupying a retained position in which the tab is retained relative to the support sleeve and a released position in which said tab stops being retained relative to the support sleeve to allow relative sliding of the protection sleeve and the support sleeve towards a protection position in which the needle is surrounded by the protection sleeve, where the plunger assembly has a cylindrical skirt suitable, at the end of the injection stroke of said plunger assembly, for coming opposite a proximal end portion of the support sleeve for engaging with an actuating part of the retaining tab for urging said tab towards the released position thereof.
In the meaning of the invention, the proximal end of an element is the one which is the closest the fingers of the user giving an injection by using the device, whereas the distal end is the opposite end.
A device of this type is known from documents EP-A 1,235,603 and EP-A 1,474,194.
In EP 1,235,603, the cylindrical skirt of the plunger assembly is thick, such that it is rigid, and has a frustruconical internal shape allowing it to come into contact with the inclined external surfaces of the two retention tabs, to bring these tabs back towards the inside, meaning towards the vertical axis of the device, so as to free them from being retained relative to the support sleeve. For the release of the tabs to occur reliably and systematically, it is necessary for the skirt to be thick and rigid and that the tabs be accessible for this skirt. Thus, the tabs are relatively remote from the central axis of the device because they are located on either side of the collar of the syringe body which serves to retain this body relative to the support sleeve.
With a device of the type described in EP 1,235,603, it is therefore necessary to use a plunger assembly which has a skirt with a particular confirmation and a large radial dimension.
In EP 1,474,194, the skirt has the shape of a portion of a cylinder whose lower end is slightly chamfered on the inner side. This time, the tabs for retaining the protection sleeve relative to the support sleeve are substantially contained in the bulk of the collar of the syringe body when they are in their retained position. Consequently, these tabs are not easily accessible for the skirt of the plunger assembly, such that relay tabs, rigidly connected with the support sleeve, are necessary. At the end of the injection, the skirt comes to bringing the relay tabs back to the inside, and these tabs engage with the tabs for retention of the protection sleeve in order to also return these latter to the inside.
In sum, the bulk of the device in the radial direction is relatively large.